Probably for when you jack the vehicle up to change a wheel. Can be very useful if you have to jack up the axle which has the handbrake as the vehicle can roll away if you are not careful and fall off the jack.

But similar things are also used with levelling ramps so you don't have to leave the handbrake on.

I had these supplied with an auto Land Rover I bought years ago, the handbook said they were to chock the wheels as you were jacking it up.
They maybe supplied with yours for the same reason because it is an auto.
No reason you can't use them for the reason you specified, but the Park position on your auto box should lock the gearbox up anyway so it shouldn't move if the handbrake fails.

I assume they have a similar ridge pattern on the underside to the ramp ridges allowing them to lock in place ?

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I don't use them that high John, I put the truck onto the ramp, then shove the wedge under the tyre, rear end of the wedge still on the ground. Any movement of the wheel 'locks' the wedge quite firmly.

'Democracy is two wolves and a lamb voting on what's for lunch'

"We sleep safely at night because rough men stand ready to visit violence on those who would harm us"
Sir Winston Churchill

'And the Good Lord did say, "Blessed is he who expects nothing, for he shall not be disappointed."

As with (apparently) the vast majority of Al-Co equipped Ducato chassis. Mine sits downhill at all times and must be parked on blocks, even on the (Level) driveway!. I use wedges too so that I can park up with the handbrake off!, saves the big "Crunch" that is the seized on brake lining coming off when it is first moved after a longish lay up!!. I`v always used blocks and or wedges to immobilise vehicles and caravans, rather than the brakes, if they are going to be parked more than a few days (even bricks in the past!).

BTW, I`ve always spelt it Wedges?. a wedgie was something eye-wateringly painful as I recollect!!